Mashed Potatoes Recipe: Potato and Celeriac Gratin

This mashed potatoes recipe is a bit more. It goes a bit above and beyond the call of duty. Everyone, almost, knows how to make plain ol’ mashed potatoes. And everyone has had them so many times that they get a bit boring. This recipe adds some rustic French gourmet flair to those old potatoes and lots of rich aromatic flavor. In the south of France, veggies are often served as gratins. No, gratin doesn’t necessarily mean just potatoes with melted cheese on them, it means any vegetable dish roasted in a shallow casserole dish called a gratin, adding a nicely browned, crusty top to your tender vegetable dish.

There are dozens of types of gratin dishes. This one is a take on the mashed potatoes recipe but with some celeriac (celery root) added in for complexity and aroma and then baked in a dish to complete the gratin. It only takes a couple of extra steps from old-fashioned basic mashed potatoes recipes but adds a whole dimension of flavor and aroma, creamy and rich but with a nice crusty top.

What You Need

  • Potatoes: Any type is fine but I like something thats pretty creamy in texture when cooked like red potatoes or yukon golds, as pictured here. For this recipe I usually skin them and cut them into quarters but you can leave some or all of the skin on if you’d prefer.
  • Celery Root (Celeriac): This root vegetable can be found in most markets. You cut off the rough exterior skin and then dice the inside.
  • Garlic: A few cloves, peeled and cut in half.
  • Heavy Cream
  • Butter
  • Salt and freshly ground black pepper

How to Cook this Mashed Potatoes Recipe

  1. Prepare the vegetables. For this mashed potatoes recipe you can alter the amounts of each depending on your taste. If you want it more like traditional mashed potatoes, use mostly potatoes with only one celery root and a bit of garlic. If you want a more aromatic and complex dish, use about equal amounts of potatoes and celeriac. Use garlic to preference but I like at least a few cloves.
  2. Prepare a large pot of salted water and bring to a boil. Place the pieces of potatoes, celeriac and garlic in the water and boil over low-medium heat. Start testing the root vegetables after about 15 to 20 minutes. The celeriac tends to take a bit longer to soften and will never be as soft as the potatoes but you want it tender enough to smash and puree.
  3. Preheat an oven broiler.
  4. When the potatoes and celeriac are soft, remove them from the water to a bowl. Reserve some of the cooking liquid.
  5. Add a few tablespoons of butter and mash the vegetables in a bowl with the back of a wooden spoon or a large fork. As the butter melts, thoroughly work it into the mashed vegetables. Add a splash of the cooking liquid and some heavy cream to obtain a softened texture, enough that it can be stirred easily but still solid.
  6. Transfer the vegetables to a food processor and purée thoroughly. Add cooking liquid, cream and/or butter as needed to obtain a smooth, creamy consistency. It should not be liquid or pourable, just soft and creamy.
  7. Transfer the purée to a casserole or gratin dish. Flatten and dimple the surface with a spatula to decorate as desired.

    mashed potatoes recipe 2
  8. Drizzle the top with olive oil or melted butter and place, uncovered, in the oven under the broiler but at least a few inches from the heat source. If it is too close to the heat the top will burn fast and won’t develop a nice golden brown crust.
  9. Cook for a few minutes but watch closely because depending on the heat and the proximity to the heat source it can burn quickly. Remove when the top has developed a nice golden brown colored crust.
  10. Remove and let cool a few minutes before serving.


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